The involvement of highly reiterated DNA (hrDNA) sequences in chromosomal evolution will be studied utilizing the unique resources of the San Diego Zoo and San Diego Wild Animal Park. Closely related species with drastically different karyotypes (e.g. Equus przewalskii, 2n equals 66 and E. zebra hartmannae, 2n equals 32) will be employed in studies of DNA sequence relatedness and cytological localization of hrDNA sequences between closely related species with divergent karyotypes. Of special interest is the relationship between centromeric (heterochromatic) hrDNA sequences of the speices with the higher diploid chromosome number to centromeric and non-centromeric heterochromatin of the related species with a reduced chromosome number.